1. Field of the Invention
The present invention relates to a pressure plate spring for biasing a pressure plate attached to a rear cover of a camera. The present disclosure related to subject matter contained in Japanese Patent Application No. 9-131510 (filed on May 21, 1997), which is expressly incorporated herein by reference in its entirety.
2. Description of the Related Art
In a conventional 35 mm film camera, etc., a pressure plate is arranged on the inner face of a rear cover of the camera to press a film against a film guide rail arranged within the camera. To bias the pressure plate against the film guide rail, a pressure plate spring which is a kind of leaf spring is arranged between the pressure plate and the rear cover. Recently, there is a case in which a photo reflector for detecting a perforation of the film is arranged in the rear cover to obtain information with respect to existence and a moving amount of the film. In this case, the photo reflector is generally arranged in a manner that it faces the film through a notch portion formed in a corner of the pressure plate.
FIG. 8 is a schematic view showing one example of the rear cover 100 into which such a photo reflector 150, the pressure plate 120 and the pressure plate spring 130 are assembled. FIG. 8 shows the rear cover 100 seen from an inner side. In FIG. 8, the running direction (hereinafter, called a film running direction 1) of an unillustrated film at the time when the rear cover 100 is closed is shown by a chain line 1.
As shown in FIG. 8, guide frames 101, 102 are respectively projected along the film running direction 1 in the vicinity of center of upper and lower edges of the inner face of the rear cover 100. In the vicinity of respective both end portions of these guide frames 101, 102, restricting claws 101a, 101b, 102a, 102b are integrally formed in such a manner that these claws are projected toward the opposite guide frames 102, 101 and that clearances of sufficient distance are put between these claws and the inner face of the rear cover 100.
The pressure plate 120 is formed in the shape of which outer edge fits between these guide frames 101, 102 and has a thickness set such that this pressure plate 120 can move between the inner face of the rear cover 100 and each of the restricting claws 101a, 101b, 102a, 102b. The corner formed by the winding spool side edge 121 (which would be located in the vicinity of the film winding spool of an unillustrated camera body at the time when the rear cover 100 is closed) (a right-hand end edge of FIG. 8) and the lower edge 122 of this pressure plate 120 is cut in a rectangular shape to arrange the photo reflector 150.
The pressure plate 120 formed in this way is inserted between the guide frames 101 and 102 from left side in FIG. 8 and between the inner face of the rear cover 100 and each of the restricting claws 110a, 101b, 102a, 102b. This pressure plate 120 comes in contact with a photo reflector unit 140 housing a photo reflector 150 and is positioned by this contact.
The pressure plate spring 130 is inserted between the rear cover 100 and the pressure plate 120 thus set each other. This pressure plate spring 130 is formed in a shape in which four leg portions 130b to 130e, a film pressing spring 130f and a fixing piece 130g are respectively extend from a central portion 130a, in advance by blanking working. The central portion 130a of the pressure plate spring 130 is closely fixed to the inner face of the rear cover 100 by a set screw 160 going through the fixing piece 130g. Each of the leg portions 130b to 130e is arranged in parallel with the film running direction 1. The leg portions 130b to 130e are arranged two by two at both of upper and lower edges of the central portion 130a. On each edge, a pair of leg portions extend in directions where they are separated from each other. These leg portions 130b to 130e are respectively bent to this side from the plane of FIG. 8 and press the pressure plate 120 against the respective restricting claws 101a, 101b, 102a, 102b or the film guide rails of an unillustrated camera body through an unillustrated film by the end tips of the leg portions, when the rear cover 100 is closed. Each of the leg portions 130b to 130e must have a sufficient length so as exert elasticity and a stroke enough to function as a spring.
However, as mentioned above, the pair of leg portions 130b, 130c and the pair of leg portions 130d, 130e are respectively arranged along the upper and lower edges of the central portion 130a of the conventional pressure plate spring 130. Accordingly, when the pressure plate 120 is cut to arrange the photo reflector 150, the length of the pressure plate 120 in the film running direction 1 is shortened, so that length of each of the leg portions 130b to 130e can not be sufficiently secured. This is a conventional first problem.
Besides, if the length of each of the two leg portions 130b to 130e arranged in the film running direction 1 is excessively secured in spite of the length of the pressure plate 120 in the film running direction 1 shortened, roots of the leg portions 130d, 130e excessively approach each other as shown in FIG. 8. As a result, a boundary portion 130h between these leg portions 130d, 103e and the central portion 130a of the pressure plate 130 becomes excessively thin so that strength of the pressure plate spring 130 itself is reduced. This is a conventional second problem.